Note
In the search for antitumor metabolites from marine sponges, a number of novel
peptides with unique structures and activities have been identified. Peptides belonging to
several structural series have been found and these peptides often contain unusual amino
acids, which are either rare in terrestrial and microbial systems or which are novel to
science. The development of new NMR techniques and chemical methods for
stereochemistry determination has assisted in the structure determination of these complex
compounds. The similarity of some of these peptides to microbial metabolites illustrates
the need for further research into the symbiotic microbial association within these organisms.